Nail polish is generally applied to fingernails or toenails as two or more layers, for example in the form of a base coat layer, one or more pigmented layers, and a top coat. It is generally desirable for each applied coat to be completely dry before the application of the next coat. However, as such sequentially achieved drying time substantially increases the total time required for a multi-coat application, it is desirable to be able to apply a secondary coat to the base coat before the base coat is completely dry. However, if the base coat dries too slowly after the application of the secondary coat, the base coat solvents can be trapped at the interface between the secondary coat and the previously applied base coat, reducing the cohesiveness of the previously applied base coat and the adherence of the secondary coat to the previously applied base coat. Thus it is desirable to provide a base coat wherein each of the solvents in the base coat can evaporate from the base coat within a reasonably short period of time and not be trapped by a secondary coat.
It has been a common practice to employ aromatic solvents, such as toluene, as one of the solvents in a nail coating composition. However, the use of toluene is now considered to be undesirable because it is toxic by ingestion, inhalation, or skin absorption, and may cause mild macrocytic anemia. Many of the solvents employed in nail coating compositions are considered to have a drying effect on human skin and nails when there is prolonged contact. Thus, it is desirable that a nail coating composition avoid the use of aromatic solvents, such as toluene, as well as provide protection against such drying effects of the solvents which are used.
Pappas et al, U.S. Pat. No. 5,206,011, discusses the prior art solvent mixtures for nail enamels and concludes that the complicated character of the nail enamel mixtures of the prior art and the many possible combinations of volatile and nonvolatile components had, until the Pappas et al discovery, made the determination of a proper solvent balance from the perspective of viscosity, solubility of the individual components and the acceptability of the deposited enamel (gloss) in combination with a drying time of less than three minutes virtually impossible. Pappas et al state that prior to their discovery, the identification of the evaporation rates of the individual solvents under various conditions had not removed the uncertainty involved in determining a suitable solvent balance incorporating quick-drying characteristics. Although the desirability of a quick-drying nail enamel had been a long-felt need, the rate of drying of the nail enamels of the prior art had been limited by these considerations. Pappas et al further conclude that prior to their discovery, simply incorporating low boiling solvents did not increase the likelihood that an acceptable solvent system for nail enamels would be found or that one could obtain a nail enamel composition which dried in under three minutes.
Pappas et al describe their discovery as being that the use of acetone in certain weight percentages of the nail enamel composition, in combination with numerous solvents which provide acceptable viscosity, creates a consistent quick-drying solvent system which provides a nail enamel with favorable characteristics of drying time, viscosity, gloss, flexibility and durability. Thus, the Pappas et al patent teaches that the only way to make it possible to determine a proper solvent balance, to remove the uncertainty involved in determining a suitable solvent balance incorporating quick-drying characteristics, to increase the likelihood that an acceptable solvent system for nail enamels would be found, or to increase the likelihood that one could obtain a nail enamel composition which dried in under three minutes, would be to employ acetone in the solvent system. The Pappas et al patent further states that the amount of the acetone should be no less than about 4.5%, and preferably no less than 13% by weight. However, the presence of significant amounts of acetone in a nail enamel composition can lower the viscosity of the nail enamel composition to such an extent that particulate ingredients are permitted to settle, thus causing an undesirable variation in the composition. Moreover, prolonged or repeated contact of the skin with acetone can dry and defat the skin and cause dermatitis.
Although the Pappas et al patent does disclose several solvent systems which do not contain acetone, the Pappas et al patent indicates that such non-acetone solvent systems do not meet the criteria. For example, the solvent system #2 (consisting of isopropanol, ethyl acetate, n-butyl acetate, and methylchloroform) employed in Example 3 had a drying time of 3 minutes and 17 seconds under specified conditions including 40% relative humidity, or a drying time of about 4.5 to 5.0 minutes at 50-55% relative humidity. Similarly, the solvent system #3 (consisting of isopropanol, ethyl acetate, and n-butyl acetate) employed in Example 4 had a drying time of 3 minutes and 9 seconds under specified conditions including 40% relative humidity, or a drying time of about 4.5 to 5.0 minutes at 50-55% relative humidity. Also, the solvent system #9 (consisting of isopropanol, ethyl acetate, toluene, n-butyl acetate, methylene chloride, and methylchloroform) employed in Example 10 had a drying time of 3 minutes and 21 seconds under specified conditions including 37% relative humidity, or a drying time of about 4.0 to 5.0 minutes at 50-55% relative humidity.
The Pappas et al patent indicates that even when the minimum amount (4.5%) of acetone was present, the drying time was longer than desirable. Thus, in the solvent system #8 (consisting of acetone, isopropanol, ethyl acetate, toluene, n-butyl acetate, and methylchloroform) employed in Example 9, the composition had a drying time of 2 minutes under specified conditions including a low 24% relative humidity, or a drying time of about 3.0 minutes at 50-55% relative humidity. Thus, the Pappas et al patent teaches that the only way in which the desired objectives can be achieved is to employ at least 4.5% acetone in the nail polish composition.
In contrast to the express teachings of the Pappas et al patent, applicant has discovered that the objectives can be achieved without the use of any ketone, such as acetone.
Nitrocellulose, or cellulose nitrate, is a thermoplastic, non-oxidizing polymer which, when cast from a solvent solution, dries by evaporation to form a film. Nitrocellulose is a commonly employed ingredient in nail coating compositions in that nitrocellulose has good hardness, good toughness, and good resistance to abrasion. However, as nitrocellulose is relatively brittle, the adhesion of the nail coating to the nail deteriorates within a few days due to the growth of the nail so that the nail coating separates from the nail. Thus, nitrocellulose does not provide the desired long lasting adhesion of the nail coating to the nail. While the combination of a toluene-sulfonamide-formaldehyde resin with nitrocellulose in a nail coating composition is considered to improve the strength and adhesion characteristics of the nail coating composition over that offered solely by the nitrocellulose, the use of formaldehyde containing resins in a nail coating is undesirable, as the formaldehyde containing resins dry the nails and make the nails brittle. Allegeties have also been reported for resins such as arylsulfonamide/formaldehyde resins. For example, in many cases of dermatitis due to nail enamel, a toluene-sulfonamide-formaldehyde resin is the etiologic agent. Thus, there is a need for a combination of polymers which provide a nail coating composition with both the desired initial adhesion and the desired long term adhesion, while avoiding the use of formaldehyde containing polymers.
It is also desirable that the base coat protect the nails against damage from ingredients in the secondary coats as well as in the base coat, e.g., ingredients which cause drying of the nails and/or skin.
Accordingly, there is a need for a nail coating composition which is substantially free to totally free of aromatic solvents and ketones, and which is substantially free to totally free of formaldehyde containing resins, but which provides a desirable level of adhesion, both initially and long term, and which provides protection for the nail against the drying effects of solvents employed in the nail coating composition.